Periodontal disease is the most common cause of tooth loss in the adult population in the U.S. In advanced periodontal lesions, plasma cells are the predominant cell type observed yet the origin and the role of these cells in the pathogenesis of the disease remains largely unknown. Although there is evidence that specific immunity to bacterial antigens may be important, recent data from our laboratory suggest that nonspecific polyclonal activation of host B-cells by substances from the dental plaque bacterium, Actinomyces viscosus (AVIS) may play an important role in the recruitment, maturation and differentiation of B-cells into plasma cells in periodontal lesions. Different polyclonal B-cell activators (PBAs) are believed to trigger distinct maturational subclasses of B-cells to synthesize DNA and/or hastened maturation depending on the activating substances. Thus, selected PBAs such as dextran sulfate (DS), lipopolysaccharide (LPS) from gram-negative bacteria and AVIS can serve as useful functional markers. As a partial explanation for the appearance of plasma cells in periodontal lesions, one possibility is that within a host B-cell subpopulations are selectively recruited, activated and driven to maturity. The aim of the proposed studies is to compare the PBA responses of B-cells in two organs; the bone marrow, in which immature B-cells predominate and the spleen, the B-cell populations of which is composed of largely mature B-cells. In both organs short-lived and long-lived mature and immature B-cells will be selectively tagged with 3H-TdR. Therefore, we can visualize directly the results of stimulation by DS, LPS and AVIS on any given subpopulation of B-cells. Blastogenesis, DNA synthesis and the expression of cytoplasmic and cell surface immunoglobulin will be used as indices of cell activation or maturation. Knowledge of the state of maturation, lifespan, and differential activation by selected PBAs may provide the rationale for the development of new therapeutic approaches in the control and treatment of periodontal and other chronic inflammatory diseases.